LONDON—British Prime Minister David Cameron has announced measures to toughen welfare rules for migrants from the European Union.

The announcement came amid rising concern in Britain that migrants from Romania and Bulgaria—who could start working without restriction in the U.K. and the rest of the EU from Jan. 1—would exploit the British welfare system.

The measures announced Wednesday include barring new migrants from getting get jobless benefits for the first three months, and deporting migrants caught begging or sleeping outdoors.

Cameron also proposed restricting the free movement of EU workers, saying the policy has caused "vast migrations" of people from poorer member states to richer ones.

His comments were criticized by European Employment Commissioner Laszlo Andor, who said they were an "unfortunate over-reaction."